Oil

Oil is a type of in game Resource that allows you to build all Advanced Ground, Air, and Navy Units. Oil is produced by Oil Wells, which have contracts bought with Coins. There are three types of Oil Wells that you can unlock by increasing your Empire’s population. More advanced Oil Wells produce more Oil. Oil can also be bought and sold on the Market.
Oil is also dropped during combat from picking up the remains of your units that have been destroyed.
However, they only drop 00000000000000000001. 1 Oil per unit lost.